1. Field of the Invention
This invention relates to color television recording and playback systems. In a primary application the invention relates to the recording of encoded television information onto film and the reading out of that information in the form of color television signals. Another application of the invention relates to the photographic recording of live scenes onto a photosensitive medium in an economic fashion and with a format which can be converted into color television signals.
2. Description of Prior Art
A variety of approaches have been used for the recording and playback of color television information. These have included magnetic tape, discs, and film. Magnetic tape systems use a very expensive media. In addition, the recording process from live scenes requires a color television camera and is thus quite expensive. Disc systems have had a variety of mechanical difficulties. In addition, the home consumer cannot record live scenes on this media. Film systems thus represent an attractive approach to the recording and playback of color television information. They are both high in information density and they can be used in modified home cameras to enable home consumers to record their own material and play it back on their home color television receivers.
Existing color television encoding formats on film have various problems. Most approaches encode the color information on a very high frequency carrier. The high fequencies are used to separate the chrominance information from the high frequency portions of the luminance information. These high frequencies are difficult to resolve on the film. In addition they are difficut to resolve on the scanner when the encoded information is read out. In addition, it is difficult to keep track of the phase of high frequency carriers so that amplitude modulation of two different carriers is usually employed. A variety of cross talk can then develop between the two modulated carriers carrying the color information, and the high frequency components of the luminance signal.
One such encoding format is described in U.S. Pat. No. 3,378,633. Monochrome Photography System for Color Television, issued to A. Macovski. In this patent the red and blue information are encoded on vertical and diagonal high-frequency carriers by projecting the color image through two striped color filters at these same angles. This system requires a relatively high resolution camera to resolve the high frequency color carriers. Also, the luminance resolution must be degraded somewhat to prevent high-frequency luminance detail from appearing in the color bandpass circuits. Thus the full luminance resolution of the system is not achieved, and a relatively high-resolution scanner is required to read out the encoded color information.
One solution to this problem is the use of separate recorded frames for the luminance and chrominance information. This is done in the EVR system. The EVR system is described in a publication by Peter C. Goldmark entitled, "Color Electronics Video Recording," which appeared in the Journal of the Society of Motion Picture and Television Engineers, Vol. 79, August, 1970, pp. 677-686. In this system an electron beam recorder records two rows of frames on film. These include a luminance frame and a chrominance frame on which a color subcarrier is amplitude-modulated by two color difference signals in phase quadrature. This system, however, is not used for producing encoded film by the consumer, since the chrominance information is not created photographically by imaging through a striped filter as in U.S. Pat. No. 3,378,633. Thus it is suitable only for pre-recorded material. In addition, the format used makes relatively inefficient use of the storage media since each film frame is used for a single television field, or half of the information required for a television frame. The pairs of luminance and chrominance frames are recorded and played back at 60 fields/sec.
The direct photographic recording of the EVR format is described in U.S. Pat. No. 3,535,992, "Method and Apparatus for Optically Recording Color Picture Information on a Photographic Medium," issued to Peter C. Goldmark and William E. Glenn. In this patent the chrominance frame is recorded by filtering the color scene using a striped color filter. A variety of dual imaging methods are shown in this patent for simultaneously imaging the color scene onto the luminance and chrominance frames. This system has the same inefficient use of film previously described.
The system described in both U.S. Pat. No. 3,535,992 and the previously described publication on the EVR system use a fairly complex method of providing continuous synchronization signals. A half-frequency reference signal is included over the entire chrominance frame to account for scan velocity errors during playback. Existing CCD line scanners are not subject to scan velocity errors. Thus they can be used with simpler synchronization formats which can be implemented much more economically. These preferred synchronization formats are not intermixed with the color information and thus do not use up part of the dynamic range of the film. In addition, the system is much less subject to film non-linearities.
The previously described systems all used frame scanners in the readout mode consisting of television cameras or flying spot scanners. These are much more expensive than line scanners. In addition, line scanners are used with continuous film motion. This type of motion is simpler to realize without requiring the rapid pulldown often used with frame scanners.